zfs very poor performance compared to ufs due to lack of cache?

[Andriy Gapon]

on 06/09/2010 14:04 Kostik Belousov said the following:
> On Mon, Sep 06, 2010 at 01:54:15PM +0300, Andriy Gapon wrote:
>> on 06/09/2010 02:57 Steven Hartland said the following:
>>> Based on Jeremy's comments I'm updating the box the stable. Its building now
>>> but will be the morning before I can reboot to activate changes as I need to
>>> deactivate the stream instance and wait for all active connections to finish.
>>>
>>> That said the problem doesn't seem to be cache + free but more cache + free
>>> + inactive with inactive being the large chunk, so not sure this change
>>> would make any difference?
>>>
>>> How does ufs deal with this, does it take inactive into account? Seems a bit
>>> silly for inactive pages to prevent reuse for extended periods when the
>>> memory could be better used as cache.
>>
>> Inactive pages are also a cache, just a different kind.
> Not quite. Inactive pages may be dirty. Such pages cannot be freed or reused
> without pageout.

Yes, they can be dirty, but I didn't say that inactive was a "clean-only" cache.
ARC entries can also be dirty and it's still a cache.

-- 
Andriy Gapon